Ultrasonic instruments, including both hollow core and solid core instruments are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect or coagulate tissue or to separate muscle tissue off bone. Ultrasonic instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the single or multiple element end effector (e.g., cutting blade, ball coagulator) of such instruments at ultrasonic frequencies induces longitudinal, transverse or tortional vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulating. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulating.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors may be designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The transducer and the end effector may be designed to resonate at two different frequencies and when joined or coupled may resonate at a third frequency. The zero-to-peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:ω=the radian frequency which equals 2π times the cyclic frequency, f, andA=the zero-to-peak amplitude.The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2A.
Ultrasonic surgical instruments may be divided into two types, single element end effector devices and multiple-element end effector devices. Single element end effector devices include instruments such as scalpels (e.g., blades, sharp hook blades, dissecting hook blades, curved blades) and ball coagulators. Single-element end effector instruments have limited ability to apply blade-to-tissue pressure when the tissue is soft and loosely supported. Substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. This inability to grasp the tissue results in a further inability to fully coapt tissue surfaces while applying ultrasonic energy, leading to less-than-desired hemostasis and tissue joining. In these cases, multiple-element end effectors may be used. Multiple-element end effector devices, such as clamping coagulators, include a mechanism to press tissue against an ultrasonic blade that can overcome these deficiencies.
One drawback of existing ultrasonic instruments is their size. The large size and bulkiness of existing ultrasonic instruments can make it more difficult for clinicians to manipulate the instruments in surgical environments where fine movement is required and can also obstruct the vision of the clinician. This may limit the usefulness of ultrasonic instruments in small surgical sites. Also, because of the bulkiness of existing transducers, many existing ultrasonic instruments position the transducer proximal from the end effector, requiring an extended, and often relatively inflexible wave guide. As a result, articulation of the end effector and blade may be difficult or impossible. This limits the usefulness of existing ultrasonic instruments in endoscopic and laparoscopic surgical environments.